Based on our recent findings on androgen receptor (AR) phosphorylation at serine 81 and AR interactions with protein phosphatase 1 (PP1), we are updating Aims 4 and 5 (ROO phase) fronri the parental grant. These two Aims will be integrated into Aim 5 of the updated proposal for the ROO phase, and a new Aim 4 will build on our recent findings made during the K99 phase examining AR serine 81 phosphorylation and AR association with chromatin. Aim 4. Characterize the higher molecular weight AR molecules that associate with AR chromatin binding and serine 81 phosphorylation. Our data suggest that serine 81 phosphorylation may target AR for further posttranslational modifications (such as monoubiquitylation or SUMO conjugation) that may be required for stable chromatin binding and transcriptional activation. Biochemical and molecular approaches will be used to test these hypotheses. Aim 5. Determine the functional importance of AR phosphorylation/ dephosphorylation and its interaction with PPip. Our initial Aims 4 and 5 proposed to study the interactions between AR and PP1. The PP1 catalytic subunit has 3 isoforms, a, p, and y, and our recent data indicate that PP1P has the greatest interaction. Therefore, the experiments have been modified to focus on regulation of AR functions by PPip.